Project I Project Summary A fundamental issue in cognitive neuroscience is how the brain encodes others? actions and intentions. In recent years, an important advance in our knowledge on how these processes may take place is the discovery of mirror neurons (MNs). The main conceptual breakthrough spurred on by their discovery is that perceptual and motor processes may share a common code. Over the past five years, as part of a Program Project, we have made a number of discoveries regarding the mirror neuron system (MNS) in human infants, children and adults. First, data from functional MRI studies suggest that there are differences in the extent of overlap in mirror areas between 8-year olds and adults, reflecting continued development of the MNS during childhood. Second, we find age differences in the magnitude of EEG mu Event Related Desynchronization (ERD) during observation of actions over central-parietal sites and as well as the emergence of a second MNS signal in the EEG, ERD in the beta frequency during middle childhood. Third, analysis of EEG coherence patterns across age suggest development of organized brain networks that continue to develop across childhood underlying an extended MNS. Fourth, individual differences in motor skills are associated with the magnitude of mu ERD during observation in infants, 4- and 8-year-old children and adults. Together, these data suggest that the MNS early in life supports the emergence of basic motor skills and learning to attend to actions, but that development continues through childhood. The specific aims for the next grant period are first, to examine the effects of experience on the MNS and its links to social-communicative gestures in infancy. Second, to use fMRI and EEG to chart the developmental trajectory and functional significance of the MNS in childhood. Through these aims we will provide an expanded and broader view of the role that the MNS plays in development of social cognition and the links between the MNS and motor competence.